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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Thu, 30 Apr 2020 00:46:57 +0200
Message-ID: <CAK8P3a0M9qh2-_5VKx89ZsTfy5S1zhfWwnO7rN4xYhDwBBvPjw@mail.gmail.com>
Subject: Re: Remaining randconfig objtool warnings, linux-next-20200428
To:     Josh Poimboeuf <jpoimboe@redhat.com>
Cc:     Peter Zijlstra <peterz@infradead.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>
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On Wed, Apr 29, 2020 at 8:55 PM Josh Poimboeuf <jpoimboe@redhat.com> wrote:
>
> On Tue, Apr 28, 2020 at 11:10:44AM -0500, Josh Poimboeuf wrote:
> > > ==> build/x86/0xE0F2ACFF_defconfig/log <==
> > > kernel/time/posix-stubs.o: warning: objtool: __x64_sys_timer_create()+0x23: sibling call from callable instruction with modified stack frame
>
> This one is fixed with the following cleanup:
>
> From: Josh Poimboeuf <jpoimboe@redhat.com>
> Subject: [PATCH] linkage: Convert syscall alias macros to C
>
> There's no need to use inline asm to create ELF alias symbols.
> Annotated C function declarations can be used instead.
>
> This also makes the ordering of the ELF symbol table more logical, with
> the real function now always coming before the aliases.  This makes it
> easier for objtool, objdump and other tools to differentiate them.
>
> This fixes the following warning:
>
>   kernel/time/posix-stubs.o: warning: objtool: __x64_sys_timer_create()+0x23: sibling call from callable instruction with modified stack frame
>
> Reported-by: Arnd Bergmann <arnd@arndb.de>
> Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> ---
>  include/linux/linkage.h | 14 ++++----------
>  1 file changed, 4 insertions(+), 10 deletions(-)

Unfortunately, this patch leads to new warnings when
CONFIG_POSIX_TIMERS is disabled:

In file included from /git/arm-soc/kernel/time/posix-stubs.c:9:
/git/arm-soc/kernel/time/posix-stubs.c:35:37: error: conflicting types
for 'sys_timer_create'
   35 | #define SYS_NI(name)  SYSCALL_ALIAS(sys_##name, sys_ni_posix_timers)
      |                                     ^~~~
/git/arm-soc/include/linux/linkage.h:26:63: note: in definition of
macro 'SYSCALL_ALIAS'
   26 | #define SYSCALL_ALIAS(alias, name) __alias(name) typeof(name) alias
      |                                                               ^~~~~
/git/arm-soc/kernel/time/posix-stubs.c:42:1: note: in expansion of
macro 'SYS_NI'
   42 | SYS_NI(timer_create);
      | ^~~~~~
In file included from /git/arm-soc/kernel/time/posix-stubs.c:13:
/git/arm-soc/include/linux/syscalls.h:616:17: note: previous
declaration of 'sys_timer_create' was here
  616 | asmlinkage long sys_timer_create(clockid_t which_clock,
      |                 ^~~~~~~~~~~~~~~~

We can probably move those SYS_NI() instances to kernel/sys_ni.c,
which does not include the header, but it's still a bit ugly. I'll try
that tomorrow
unless you come up with a better suggestion first.

        Arnd